An electronically controlled throttle control apparatus has a throttle valve to open and close the bore of throttle body by the torque of a drive motor shaft, and an engine control apparatus to control the engine rotation speed by driving the drive motor depending on the driver's accelerator pedal depression to set the opening degree of the throttle valve to a specific opening degree. In the electronically controlled throttle control apparatus, the gear case is integrally formed on the outer wall surface of the throttle body. The gear case rotatably houses the following gears as components of a transmission system which transmits the torque of the drive motor to the throttle shaft: a valve-side gear (driven gear) fixed to one end of the throttle shaft which rotates integrally with the throttle valve; a motor-side gear (drive gear) fixed to one end of the drive motor shaft; and an intermediate gear, located between the valve-side gear and the motor-side gear, which rotates around the intermediate shaft.
This construction is intended to provide an opener function (default spring function or limp-home function) which enables a car to move to a safe place without a sudden engine stop even if an electrical current to the drive motor is interrupted for some reason. Here the opener function is provided by using different spring forces of plural coil springs to mechanically hold the throttle valve in a prescribed intermediate position (intermediate stopper position) between its full close position and full open position. This constructions is disclosed in, for example, EP 0992662 A2 (JP-A-2000-110589).
This electronically controlled throttle control apparatus has a double coil spring structure. In double coil spring structure, the terminal hooks of both a first spring as a return spring and a second spring as a default spring are held on an intermediate stopper member which is housed in the gear case and in an intermediate stopper position. The ends of the first and second springs are wound in different directions. The valve-side gear, the motor shaft of the drive motor, the motor-side gear, and the intermediate gear are arranged in a displaced manner with respect to the throttle shaft. Given this arrangement, the size of the gear case of the electronically controlled throttle control apparatus is decreased in the longitudinal direction (for example, in the vertical direction), the direction being perpendicular to the direction of the intake air flow. It is to be noted that the opening of the gear case is closed by the gear cover in a liquid-tight manner.
However, in the above electronically controlled throttle control apparatus, the bore inside diameter of the throttle body, the outside diameter of the throttle valve and the shape of the valve-side gear have to be varied depending on the engine displacement, car model, etc. or the drive motor rotation direction. Here, the bore inside diameter of the throttle body is adopted in the range from 40 mm to 80 mm depending on the difference of engine displacements. This gives indication of a possibility that the same gear cover, intermediate gear and motor-side gear as components housed in the gear case are commonly used regardless of the engine displacement or car model. In other words, they are commonly used even when the bore inside diameter of the throttle body or the drive motor rotation direction differs.
However, even when the bore inside diameter of the throttle body is identical, it has been difficult to commonly use the same components to be housed in the gear case integrally formed on the outer wall surface of the throttle body, regardless of the engine displacement or car model, for the following reasons.
The rotation direction of the drive motor and the valve-side gear is different between the right-hand drive car and the left-hand one. The former has a steering mechanism on the right in the car body longitudinal direction, and the latter has a steering mechanism on the left. The arrangement of the components in the gear case of the former and that of the latter are symmetric, or mirror images of each other with respect to the longitudinal centerline of the gear case. This means that the full open position stopper and the intermediate position stopper as well as the return spring terminal hook and the default spring terminal hook are positionally different. Besides, the winding direction of two coil springs should be different and the shape of the valve-side gear should be different and these components should be designed for each model.